Challenges in measuring measles case fatality ratios in settings without vital registration

Measles, a highly infectious vaccine-preventable viral disease, is characterized by clustering of cases that occur during cyclical epidemics [1]. In many parts of the world, measles is also a seasonal disease with fewer cases found during the non-measles season [2]. Clinically, the infection is expressed as a maculopapular rash accompanied by fever and at least one of the three "c's": cough, coryza and conjunctivitis; virtually all cases of measles are clinically expressed [3,4]. Measles is a potentially fatal disease [1]. The World Health Organization (WHO) defines a measles-associated death as one occurring within 30 days of rash onset, not obviously due to another cause such as trauma [5].Historically, measles case fatality ratios (CFRs) have been reported to vary from 0.1% [1] in the developed world to as high as 30% among refugee populations [6,7]. Current estimates of CFRs used by WHO in endemic countries range between 0.05% - 6% [8-10]. Factors thought to affect CFR include age [11], intensity of exposure to measles virus (for which household crowding may be seen as a surrogate) [12], measles vaccination status [13], nutritional status [14], immunodeficiency [15] and access to appropriate case management [16]. Studies conducted in the late 1980 s demonstrated that supplementation of measles case-patients with vitamin A could decrease measles mortality by as much as 64% [17,18] leading to recommendations by WHO and United Nations Children's Fund (UNICEF) in 1987 to treat all measles case-patients with vitamin A in areas where measles CFRs were greater than 1% [19]. These recommendations, in conjunction with the rollout of Integrated Management of Childhood Illness (IMCI) guidelines in the mid 1990 s [20] which target pneumonia and diarrhea, might be anticipated to have decreased measles CFRs since the 1990 s. However, few data exist on the extent to which these interventions are used in health facilities, particularly in countries that are highly endemic for m